a(n) = 10^n - 9^n - 8^n - 7^n + 3*6^n.

Terms

a(0) =1a(1) =4a(2) =14a(3) =64a(4) =830a(5) =14704a(6) =228734a(7) =3136144a(8) =39450110a(9) =468241264a(10) =5338397054a(11) =59140070224a(12) =641540046590